The invention relates to a moving image correcting circuit of a display device that displays a multitonal image by time-sharing one frame into plural subfields (or subframes) and emitting the subfields corresponding to the luminance level of an input image signal.
Display devices using a PDP (Plasma Display Panel) and a LCD (Liquid Crystal Panel) have been attracting public attention as thin, light-weight display units. Completely different from the conventional CRT driving method, the driving method of this PDP is a direct drive by a digitalized image input signal. The luminance tone as emitted from the panel face depends therefore on the number of bits of the signal to be processed.
The PDP may roughly be divided into AC and DC types whose fundamental characteristics differ from each other. In any AC type PDP, sufficient characteristics have been obtained with respect to its luminance and service life. As for the tonal display, however, a 64-tone display was the maximum reported from the trial manufacture level. Recently, a future 256-tone method by Address/Display Separation type drive method (ADS subfield method) has been proposed.
FIGS. 1(a) and (b) show the exemplary drive sequence and drive waveform of the PDP used in this ADS subfield method with 8 bits and 256 tones.
In FIG. 1(a). one frame is composed of eight subfileds SF1, SF2, SF3, SF4, SF5, SF6, SF7, and SF8 whose relative ratios of luminance are 1, 2, 4, 8, 16, 32, 64, and 128 respectively. Combination of this luminance of eight screens enables a display in 256 tones.
In FIG. 1(b), the respective subfields are composed of the address duration that writes one screen of refreshed data and the sustaining duration that defines the luminance level of these subfields. In the address duration, a wall charge is formed initially at each pixel simultaneously over all the screens, and then the sustaining pulses are given to all the screens for display. The brightness of the subfield is proportional to the number of sustaining pulses to be set to the predetermined luminance. A two hundred and fifty-six tone display is thus actualized.
The foregoing display unit of address/display separation type drive method was conventionally provided with such a moving image correcting circuit as shown in FIG. 2 in order to reduce the visual display deviation resulting from the display of a moving image. The moving image correcting circuit shown in FIG. 2 comprised the moving image correcting portion 11 and the motion vector detecting portion 10, which in turn consisted, as shown in FIG. 3, of the frame memory 12, correlation value operation part 13 and motion vector generating portion 14.
In the motion vector detecting portion 10, the respective components act as follows. Based on the image signal as input into the input terminal 15, the frame memory 12 makes an image signal by one frame before the current frame picture (referred to as xe2x80x9cpreceding frame picturexe2x80x9d). The correlation value operation part 13 sequentially seeks after the correlation values (differential values) of the image signal for all the blocks in the detection area of the motion vectors in the preceding frame, referring to the block forming the subject of the current frame picture (the block consisting of a single or plural pixels, 2xc3x972 pixels, for example). The motion vector generating portion 14 generates a displacement vector (a signal representing displacement direction and displacement amount) whose starting point and end point are the block position of the preceding frame picture where the correlation value is minimal and the origin of the motion vector (the block position of the preceding frame picture at a position corresponding to the block of current frame picture) respectively. The motion vector generating portion 14 generates this displacement vector as a motion vector of the block forming the subject.
In the moving image correcting portion 11, the image signal as input into the input terminal 15 was corrected on the basis of the detected value of the motion vector detecting portion 10 (namely, the motion vector). The image signal thus corrected was output to the PDP (not shown) through the intermediary of the output terminal 16. The moving image was thus corrected by correcting the display position of each subfield for the pixels in the subject block.
We will now describe in detail how the correlation value operation part 13 in the motion vector detecting portion 10 operates the correlation values. For purpose of discussion, we assume here that, as shown in FIGS. 4(a) and (b), the detection area KR of the motion vector of the preceding frame picture has 25 blocks (5xc3x975 blocks) and that the image (pictorial image) that was at the position of the block ZB51 in this detection area KR has now displaced to the position of the block GB33 in the current frame picture. Further, it is assumed that the blocks ZB11 to ZB65 of the preceding frame picture and the blocks GB11 to GB55 of the current frame picture are formed respectively with 2xc3x972 pixels (or as many dots).
If the subject block of the current frame picture is GB33, the correlation value operation part 13 will sequentially compute, by the following expression,
S=|A1xe2x88x92A2|+|B1xe2x88x92B2|+|C1xe2x88x92C2|+|D1xe2x88x92D2|
the correlation values of an image signal for all the blocks ZB11 to ZB55 in the detection area KR of the preceding frame picture referring, as datum, to this block GB33, all along the direction shown by the alternate long and two short dashed line arrow in FIG. 4(a).
In the formula, A1, B1, C1, and D1 represent the luminance levels of the pixels forming the respective blocks of preceding frame picture ZB11 to ZB55 as shown in FIG. 5(a), while A2, B2, C2, and D2 indicate the luminance levels of the pixels forming the subject block of current frame picture GB33 as shown in FIG. 5(b).
The motion vector generating portion 14 compares the plural correlation values as obtained in the correlation value operation part 13 with each other, and generates, as shown by the thick lines in FIG. 4(b), the displacement vector MV whose starting and end points are respectively the position of the block B51 of the preceding frame picture where the correlation value is minimal and the origin of the motion vector (block ZB33 position of preceding frame picture corresponding to the block GB33 in the current frame picture). The motion vector generating portion 14 then outputs this vector MV as the motion picture of the subject block GB33.
The motion vectors can be obtained in a similar fashion also for other blocks (for instance, GB11 or GB55) of the current frame picture, when the motion vector detection area KR of the preceding frame picture embraces 25 peripheral blocks (5xc3x975 blocks) centered around the corresponding origin (for example, positions of the blocks of preceding frame picture ZB11 or ZB55 corresponding to the block GB11 or GB55).
Since, however, the block position corresponding to the least correlation value does not always coincide with the starting point (or end point) of the displacement vector if any dispersion appears in the correlation value as obtained from the correlation value operation part 13 due, for example, to the noise in the input image signal or to the fluctuation of the input image signal, there were some cases where erroneous motion vectors were detected that differed from the intrinsic motion vectors representing the motion as viewed by humans.
For simplicity, we may assume that the detection area KR of a preceding frame picture is 9xc3x979=81 blocks and that the correlation values obtained from the correlation value operation part 13 for the blocks ZB11 to ZB99 in this detection area KR is as shown in FIG. 6. Let us also assume that a correlation value, out of those in FIG. 6, for the block ZB65 near the origin of the preceding frame picture (block ZB55 position at vertical vector xe2x80x9c0xe2x80x9d and horizontal vector xe2x80x9c0xe2x80x9d) changes from intrinsic xe2x80x9c0xe2x80x9d to xe2x80x9c10xe2x80x9d and the correlation value for the block ZB82 away from the origin changes from intrinsic xe2x80x9c20xe2x80x9d to xe2x80x9c9xe2x80x9d, both by reason of noise, fluctuation or the like. Under these conditions, the motion vector generating portion 14 compares the correlation values shown in FIG. 6 with each other, and generates and outputs a motion vector whose starting point and end point are respectively the block ZB82 position corresponding to the least correlation value xe2x80x9c9xe2x80x9d and the origin. Namely, as shown in FIG. 6, not the motion vector with horizontal vector xe2x80x9c0xe2x80x9d and vertical vector 1 with, as the starting point, the block B65 position corresponding to the intrinsic least correlation value xe2x80x9c0xe2x80x9d, but an erroneous motion vector with horizontal vector xe2x80x9cxe2x88x923xe2x80x9d and vertical vector xe2x80x9c3xe2x80x9d with the block B82 as starting point is output.
The conventional art was therefore problematical in that the moving image correction conversely worsens the picture qualify if the moving image is corrected by the moving image correcting portion 11 based on the foregoing erroneous motion vector.
Let us take it for granted that, for example as shown in FIGS. 7(a) and (b), in the nine blocks (3xc3x973 blocks) B11 to B33, the detected value of the motion vector of the central block B22 changes from xe2x80x9c2xe2x80x9d or xe2x80x9c3xe2x80x9d to xe2x80x9c5xe2x80x9d due to the influence of noise, fluctuation or the like, and that the detected values of the motion vectors of the 8 peripheral blocks B11 to B33 (except B22) remain xe2x80x9c2xe2x80x9d or xe2x80x9c3xe2x80x9d without being affected by any noise or fluctuation. Then, for any pixels in the eight peripheral blocks B11 to B33 (except B22) the moving image can be corrected on the basis of a correct detected values xe2x80x9c2xe2x80x9d or xe2x80x9c3xe2x80x9d while for any pixels in the central block B22 the moving image correction is committed on the basis of erroneously detected value xe2x80x9c5xe2x80x9d. Thus, the prior art was problematical in that, ironically, the correction of the moving image caused the picture quality to be degraded.
It is also to be assumed that, as shown in FIG. 8, there is no motion vector detected (no motion) for the three blocks B13, B22, and B33 influenced by noise, fluctuation or the like out of the nine (3xc3x973 blocks) B11 to B33, and that motion vectors are detected (hatched portions in the figure) for the six remaining blocks B11, B12, B21, B23, B31 and B32 without any influence of noise or fluctuation. Then, the moving image correction intended for enhancing the picture quality may be performed for the pixels in the six blocks B11, B12, B21, B23, B31 and B32 from which the motion vectors have been detected, but no moving image can be corrected for any pixels in the three blocks B13, B22, and B33 from which no motion vector has been detected. The result was the same. That is, such a moving image correction was problematical in that it conversely caused the degradation of the picture quality.
The invention, made in light of the foregoing problematical points, is intended to prevent the picture quality from worsening due to the noise in or fluctuation of an input image signal if the moving image is corrected to reduce any visual display deviation engendered when displaying the moving image in a display device that displays a multitonal image by time-sharing one frame into plural subfields and emitting the subfields corresponding to the luminance level of an input image signal.
The moving image correction circuit by the first invention is characterized in that in a display device that displays a multitonal image by time-sharing one frame into plural subfields and emitting the subfields corresponding to the luminance level of an input image signal, said circuit has a motion vector detecting portion that detects the motion vector in a single frame or inter-frame blocks (for instance, 2xc3x972 pixels) on the basis of said input image signal, and the moving image correcting portion that outputs, to said display device, the signal which corrected the display position of respective subfields for the pixels in the blocks, based on the detected value of said motion vector detecting portion, wherein said motion vector detecting portion has a correlation value operation portion that operates the correlation values of the image signal corresponding to all the blocks in the detection area of the preceding frame picture on the basis of the blocks forming the subject of the current frame picture, a least correlation value detecting portion that detects the least correlation value S1 having the highest correlation among the plural correlation values as obtained in said correlation value operation portion, a multiplier that multiplies this least correlation value S1 by a coefficient k (k greater than 1), a correlation value converting portion that converts the correlation values not more than the multiplied value kxc3x97S1 from among the plural correlation values as obtained in the correlation value operation portion into a set correlation value S2 (S2xe2x89xa6S1) and outputs this value S2, and a motion vector generating portion that detects the correlation value corresponding to the block the nearest to the origin from among the set correlation values S2 as output from said correlation value converting portion, generates a displacement vector whose starting point and end point are the block position corresponding to said detected correlation value and the origin respectively, and outputs this displacement vector as a motion vector.
For ease of explanation, let us consider a case where the correlation value obtained in the correlation value operation part suffers a dispersion due to noise, fluctuation or the like, the least correlation value S1 (9 for example) detected from the least correlation value detecting portion is that corresponding to an erroneous block away from the origin, and the intrinsic least correlation value (xe2x80x9c0xe2x80x9d for example) corresponding to a block near the origin changes into a correlation value S1a (for example, xe2x80x9c10xe2x80x9d) larger than S1. In such a similar, conventional case as shown in FIG. 6, an erroneous motion vector is detected whose starting and end points are the block position corresponding to the least correlation value S1 and the origin respectively. In our case, however, such an erroneous motion vector is kept from being detected by the first invention. That is, the correlation value converting portion converts the correlation value not larger than the multiplied value Kxc3x97S1 (1.5xc3x97S1 for example) from among the correlation values obtained in the correlation value operation part, into a set correlation value S2 not larger than S1 (xe2x80x9c0xe2x80x9d for example) to include the correlation value S1a before the conversion in the least correlation value (S2) forming the subject of detection.
The motion vector generating portion detects the correlation value corresponding to the block the nearest to the origin from among plural least correlation values (corresponding to the correlation value S1a before the conversion), and generates a displacement vector whose starting point and end point are the block position corresponding to said detected correlation value and the origin respectively and outputs this displacement vector as a motion vector. This configuration may prevent the motion vector detecting portion from outputting an erroneous motion vector due to noise, fluctuation or the like, avoiding thus the degradation of picture quality in the correction of moving images in the moving image correcting portion.
The moving image correction circuit of the second invention is characterized in that in a display device that displays a multitonal image by time-sharing one frame into plural subfields and emitting the subfields corresponding to the luminance level of an input image signal, said circuit has a motion vector detecting portion that detects the motion vector in a single frame or inter-frame blocks based on the input image signal, a majority processing portion that seeks after the most numerous identical detected values from among the detected values detected by the motion vector detecting portion for all the blocks within the set range S including the subject block, and a moving image correcting portion that outputs, to said display device, the signal which corrects the display position of respective subfields of the pixels in the subject block, based on the detected value as obtained in said majority processing portion.
We now consider a case where one frame is time-shared into n number of subfields SFn to SF1 to display a multitonal image of n bits of an input image signal. The motion vector detecting portion detects the displacement direction (upward on the screen, for example) and displacement amount (5 dots or 5 pixels per frame) of inter-frame blocks (that is, detects the motion vector). The majority processing portion seeks after the most numerous, identical detected values from among the detected values by the motion vector detecting portion for the blocks within the set range S. The moving image correcting portion corrects the input image signal based on the detected value as obtained in the majority processing portion and outputs this signal as corrected to the display device. This configuration allows the majority processing to eliminate an uneven motion vector even if the motion vector detecting portion outputs any erroneous motion vectors due to noise, fluctuation or the like, thereby keeping the picture quality from being degraded in the moving image correcting process.
The moving image correction circuit of the third invention is characterized in that in a display device that displays a multitonal image by time-sharing one frame into plural subfields and emitting the subfields corresponding to the luminance level of the input image signal, said circuit has a motion vector detecting portion that detects the motion vector in a single frame or inter-frame blocks on the basis of the input image signal, a majority processing portion that seeks after the most numerous identical detected values from among the values detected by the motion vector detecting portion for all the blocks within the set range S including the subject block, a vertical/horizontal/oblique detecting portion that detects whether or not the blocks having identical detected values by the motion vector detecting portion have been continuously arranged vertically, horizontally or obliquely within the set range S including the subject block and outputs the identical detected values when detecting, a selector that selects the detected values as output from this vertical/horizontal/oblique detecting portion if there is any detection output therefrom and selects the detected values obtained in the majority processing portion if there is no such detection output, and a moving image correcting portion that outputs, to said display device, the signal which corrected the display position of respective subfields of the pixels in the subject block, based on the detected value as selected by this selector.
As is the case with the foregoing second invention, this configuration, namely the third invention allows the majority processing to eliminate uneven motion vectors even if the motion vector detecting portion outputs any erroneous motion vectors due to noise, fluctuation or the like, thereby keeping the picture quality from being degraded in the moving image correcting process. Since this third invention is so designed that, when an image with one respective vertical, horizontal and oblique lines moves toward a predetermined direction, the detected values of this image with vertical, horizontal and oblique lines are made to supersede, by means of the detection output of the vertical/horizontal/oblique detecting portion, the detection values obtained by majority processing, an exact moving image correction can be performed deep in detail into the image.
The moving image correction circuit of the fourth invention is characterized in that in a display device that displays a multitonal image by time-sharing one frame into plural subfields and emitting the subfields corresponding to the luminance level of the input image signal, said circuit has a motion vector detecting portion that detects the motion vector in a single frame or inter-frame blocks on the basis of the input image signal, a motion vector delaying portion that seeks after the motion vector of each block in the set range S consisting of the subject block and peripheral blocks by delaying the detection value of said motion vector detecting portion, a motion vector counting portion that counts the number of the blocks detected as having motion vectors in all the blocks within the set range S, a count comparing portion that compares if the count by said motion vector counting portion is superior to the set value or not, a motion vector embedding portion that outputs the motion vector based on the output from the motion vector delaying portion and that of the count comparing portion, and a moving image correcting portion that outputs to the display device the signal which corrects the display position of each subfield of pixels within the subject block on the basis of the motion vector as output from said motion vector embedding portion, wherein said motion vector embedding portion outputs, as the motion vector of the subject block, the blocks of the motion vectors detected as having motion vectors within the set range S, when there is no motion vector of subject block as obtained in the motion vector delaying portion and that the count comparing portion is sending out a comparison signal, and otherwise outputs the motion vector of the subject block as obtained in the motion vector delaying portion.
When there is no motion vector of the subject block as obtained from the motion vector delaying portion and the count comparing portion is sending out a comparison signal, the motion vector embedding portion outputs, as the motion vector, and to the moving correcting portion, the motion vector of the blocks detected as having the motion vector in the set range S. That is, when the number of the blocks detected as having a motion vector in the set range S is superior to the set value, the motion vector of the subject block is embedded (substituted) with the motion vector of the blocks detected as having a motion vector even if there is no motion vector of the subject block. This makes it possible that the display position of each subfield may be corrected for the pixels in the subject block on the basis of the motion vector as embedded by the motion vector embedding portion, even if the motion vector has not been detected by reason of noise, fluctuation or the like, despite the very existence of the motion vector. The dispersion in the subject block and peripheral blocks being thus annihilated, the moving image can be corrected without deteriorating the picture quality.
The moving image correcting portion of the 5th, 6th and 7th inventions replacing the motion vector detecting portion, one of the components of the foregoing 2nd, 3rd, and 4th inventions, with the motion vector detecting portion, one of the components of the first invention, prevents any erroneous motion vector from being output from the upstream motion vector detecting portion. At the same time, the downstream circuit keeps any erroneous motion vector from entering the moving image correcting portion, even when an erroneous motion vector may come out of the motion vector detecting portion. This configuration makes it possible to keep, with higher precision, the picture quality from being degraded in the correction of a moving image by the moving image correcting portion.